Rushing around at low heights and high speed over the sea is very dangerous and if you have to ask how low how fast etc don't bother! Think about visial illusions created by (for example) large/small waves, long/short swell, tail/headwind (different IAS/G/S relatioship gives different perception of height) etc etc. Light aircraft don't have radalts and I cant reliably judge my height over the sea (I was a Navy pilot for 23 years).
Sorry to sound like a killjoy but I'd rather that than read about annother funeral. I lost several friends over my career in the Navy who flew just a little bit too low!
CRX is a professional pilot who will have had specific training in low level operations and I bet his aeroplane has a radalt, I also bet that if the radalt is U/S he has pretty strict ilmits on his minimum height!
Happy landings
3 Point